mm: Make compound_pincount always available

Move compound_pincount from the third page to the second page, which
means it's available for all compound pages.  That lets us delete
hpage_pincount_available().

On 32-bit systems, there isn't enough space for both compound_pincount
and compound_nr in the second page (it would collide with page->private,
which is in use for pages in the swap cache), so revert the optimisation
of storing both compound_order and compound_nr on 32-bit systems.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>

1 files changed, 8 insertions, 13 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index e3f8755f65ed..c64bd0b67d75 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -887,17 +887,6 @@ static inline void destroy_compound_page(struct page *page)
 	compound_page_dtors[page[1].compound_dtor](page);
 }
 
-static inline bool hpage_pincount_available(struct page *page)
-{
-	/*
-	 * Can the page->hpage_pinned_refcount field be used? That field is in
-	 * the 3rd page of the compound page, so the smallest (2-page) compound
-	 * pages cannot support it.
-	 */
-	page = compound_head(page);
-	return PageCompound(page) && compound_order(page) > 1;
-}
-
 static inline int head_compound_pincount(struct page *head)
 {
 	return atomic_read(compound_pincount_ptr(head));
@@ -905,7 +894,7 @@ static inline int head_compound_pincount(struct page *head)
 
 static inline int compound_pincount(struct page *page)
 {
-	VM_BUG_ON_PAGE(!hpage_pincount_available(page), page);
+	VM_BUG_ON_PAGE(!PageCompound(page), page);
 	page = compound_head(page);
 	return head_compound_pincount(page);
 }
@@ -913,7 +902,9 @@ static inline int compound_pincount(struct page *page)
 static inline void set_compound_order(struct page *page, unsigned int order)
 {
 	page[1].compound_order = order;
+#ifdef CONFIG_64BIT
 	page[1].compound_nr = 1U << order;
+#endif
 }
 
 /* Returns the number of pages in this potentially compound page. */
@@ -921,7 +912,11 @@ static inline unsigned long compound_nr(struct page *page)
 {
 	if (!PageHead(page))
 		return 1;
+#ifdef CONFIG_64BIT
 	return page[1].compound_nr;
+#else
+	return 1UL << compound_order(page);
+#endif
 }
 
 /* Returns the number of bytes in this potentially compound page. */
@@ -1269,7 +1264,7 @@ void unpin_user_pages(struct page **pages, unsigned long npages);
  */
 static inline bool page_maybe_dma_pinned(struct page *page)
 {
-	if (hpage_pincount_available(page))
+	if (PageCompound(page))
 		return compound_pincount(page) > 0;
 
 	/*